Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
tjh.dev
kernel
os
linux
x86: Add structs and functions for paravirt clocksource
This patch adds structs for the paravirt clocksource ABI
used by both xen and kvm (pvclock-abi.h).
It also adds some helper functions to read system time and
wall clock time from a paravirtual clocksource (pvclock.[ch]).
They are based on the xen code. They are enabled using
CONFIG_PARAVIRT_CLOCK.
Subsequent patches of this series will put the code in use.
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>
authored by Gerd Hoffmann and committed by Avi Kivity 7af192c9 a9b21b62
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arch/x86/Kconfig
+4
arch/x86/Kconfig
+1
arch/x86/kernel/Makefile
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arch/x86/kernel/Makefile
+141
arch/x86/kernel/pvclock.c
+141
arch/x86/kernel/pvclock.c
···
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/* paravirtual clock -- common code used by kvm/xen
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, write to the Free Software
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Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
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*/
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#include <linux/kernel.h>
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#include <linux/percpu.h>
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#include <asm/pvclock.h>
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/*
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* These are perodically updated
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* xen: magic shared_info page
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* kvm: gpa registered via msr
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* and then copied here.
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*/
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struct pvclock_shadow_time {
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u64 tsc_timestamp; /* TSC at last update of time vals. */
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u64 system_timestamp; /* Time, in nanosecs, since boot. */
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u32 tsc_to_nsec_mul;
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int tsc_shift;
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u32 version;
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};
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/*
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* Scale a 64-bit delta by scaling and multiplying by a 32-bit fraction,
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* yielding a 64-bit result.
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*/
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static inline u64 scale_delta(u64 delta, u32 mul_frac, int shift)
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{
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u64 product;
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#ifdef __i386__
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u32 tmp1, tmp2;
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#endif
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if (shift < 0)
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delta >>= -shift;
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else
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delta <<= shift;
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#ifdef __i386__
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__asm__ (
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"mul %5 ; "
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"mov %4,%%eax ; "
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"mov %%edx,%4 ; "
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"mul %5 ; "
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"xor %5,%5 ; "
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"add %4,%%eax ; "
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"adc %5,%%edx ; "
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: "=A" (product), "=r" (tmp1), "=r" (tmp2)
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: "a" ((u32)delta), "1" ((u32)(delta >> 32)), "2" (mul_frac) );
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#elif __x86_64__
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__asm__ (
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"mul %%rdx ; shrd $32,%%rdx,%%rax"
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: "=a" (product) : "0" (delta), "d" ((u64)mul_frac) );
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#else
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#error implement me!
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#endif
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return product;
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}
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static u64 pvclock_get_nsec_offset(struct pvclock_shadow_time *shadow)
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{
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u64 delta = native_read_tsc() - shadow->tsc_timestamp;
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return scale_delta(delta, shadow->tsc_to_nsec_mul, shadow->tsc_shift);
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}
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/*
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* Reads a consistent set of time-base values from hypervisor,
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* into a shadow data area.
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*/
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static unsigned pvclock_get_time_values(struct pvclock_shadow_time *dst,
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struct pvclock_vcpu_time_info *src)
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{
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do {
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dst->version = src->version;
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rmb(); /* fetch version before data */
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dst->tsc_timestamp = src->tsc_timestamp;
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dst->system_timestamp = src->system_time;
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dst->tsc_to_nsec_mul = src->tsc_to_system_mul;
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dst->tsc_shift = src->tsc_shift;
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rmb(); /* test version after fetching data */
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} while ((src->version & 1) || (dst->version != src->version));
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return dst->version;
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}
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cycle_t pvclock_clocksource_read(struct pvclock_vcpu_time_info *src)
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{
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struct pvclock_shadow_time shadow;
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unsigned version;
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cycle_t ret, offset;
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do {
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version = pvclock_get_time_values(&shadow, src);
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barrier();
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offset = pvclock_get_nsec_offset(&shadow);
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ret = shadow.system_timestamp + offset;
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barrier();
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} while (version != src->version);
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return ret;
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}
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void pvclock_read_wallclock(struct pvclock_wall_clock *wall_clock,
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struct pvclock_vcpu_time_info *vcpu_time,
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struct timespec *ts)
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{
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u32 version;
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u64 delta;
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struct timespec now;
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/* get wallclock at system boot */
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do {
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version = wall_clock->version;
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rmb(); /* fetch version before time */
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now.tv_sec = wall_clock->sec;
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now.tv_nsec = wall_clock->nsec;
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rmb(); /* fetch time before checking version */
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} while ((wall_clock->version & 1) || (version != wall_clock->version));
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delta = pvclock_clocksource_read(vcpu_time); /* time since system boot */
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delta += now.tv_sec * (u64)NSEC_PER_SEC + now.tv_nsec;
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now.tv_nsec = do_div(delta, NSEC_PER_SEC);
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now.tv_sec = delta;
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set_normalized_timespec(ts, now.tv_sec, now.tv_nsec);
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}
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include/asm-x86/pvclock-abi.h
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include/asm-x86/pvclock-abi.h
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#ifndef _ASM_X86_PVCLOCK_ABI_H_
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#define _ASM_X86_PVCLOCK_ABI_H_
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#ifndef __ASSEMBLY__
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/*
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* These structs MUST NOT be changed.
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* They are the ABI between hypervisor and guest OS.
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* Both Xen and KVM are using this.
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*
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* pvclock_vcpu_time_info holds the system time and the tsc timestamp
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* of the last update. So the guest can use the tsc delta to get a
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* more precise system time. There is one per virtual cpu.
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*
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* pvclock_wall_clock references the point in time when the system
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* time was zero (usually boot time), thus the guest calculates the
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* current wall clock by adding the system time.
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*
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* Protocol for the "version" fields is: hypervisor raises it (making
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* it uneven) before it starts updating the fields and raises it again
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* (making it even) when it is done. Thus the guest can make sure the
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* time values it got are consistent by checking the version before
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* and after reading them.
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*/
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struct pvclock_vcpu_time_info {
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u32 version;
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u32 pad0;
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u64 tsc_timestamp;
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u64 system_time;
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u32 tsc_to_system_mul;
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s8 tsc_shift;
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u8 pad[3];
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} __attribute__((__packed__)); /* 32 bytes */
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struct pvclock_wall_clock {
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u32 version;
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u32 sec;
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u32 nsec;
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} __attribute__((__packed__));
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#endif /* __ASSEMBLY__ */
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#endif /* _ASM_X86_PVCLOCK_ABI_H_ */
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include/asm-x86/pvclock.h
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include/asm-x86/pvclock.h
···
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#ifndef _ASM_X86_PVCLOCK_H_
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#define _ASM_X86_PVCLOCK_H_
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#include <linux/clocksource.h>
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#include <asm/pvclock-abi.h>
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/* some helper functions for xen and kvm pv clock sources */
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cycle_t pvclock_clocksource_read(struct pvclock_vcpu_time_info *src);
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void pvclock_read_wallclock(struct pvclock_wall_clock *wall,
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struct pvclock_vcpu_time_info *vcpu,
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struct timespec *ts);
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#endif /* _ASM_X86_PVCLOCK_H_ */